In signal transmission via a long-distance signal line, a pre-emphasis technique of amplifying the signal on the transmitting side and transmitting the amplified signal is known (for example, Japanese Patent Application Laid-Open No. 63-156437).
FIGS. 8A and 8B are explanatory diagrams of the pre-emphasis technique. FIG. 8A illustrates a general transmission form, and FIG. 8B shows data transmission using the pre-emphasis technique. In FIG. 8A, reference numeral 801 denotes a driver of transmitting-side; and numeral 802 denotes a receiver. In this example, a signal transmitted as a rectangular wave from the driver 801 is received as a blunt (leading and trailing edges are rounded) signal by the receiver 802.
On the other hand, in FIG. 8B, a signal inputted into a driver 803 is previously subjected to edge emphasis. Then a signal outputted from the driver 803 is received by a receiver 804 as a signal close to the original rectangular wave signal. In this manner, on the transmitting side, the edge emphasis is performed on a signal before the signal is transmitted, thereby the waveform quality on the receiving side can be improved.
Particularly, when serial data transmission/reception is performed for the sake of reduction of the number of signal lines, to transmit/receive larger amount of data, it is necessary to increase a frequency for transmitting the serial data. However, upon transmitting the serial data via a long-distance signal line, if the transmission frequency is increased, the blunting of the signal as shown in FIG. 8A appears as a shift from leading edge or trailing edge of a synchronizing clock, and there is a probability that accurate data transmission cannot be ensured.
Generally, on the transmitting side, signal amplification by pre-emphasis is performed and the amplified signal is transmitted as shown in FIG. 8B, thereby timing margin in the serial signal is ensured in the use of serial transmission method.
However, as the pre-emphasis amplifies high frequency components such as leading and trailing edges of a signal, radiation noise is generated, and electric consumption is increased by electricity amplification.